1. Field of the Invention
The present invention relates to a biological information processing apparatus for processing or measuring biological information regarding a living body, such as pulse wave, more particularly to a biological information processing apparatus capable of estimating the age of blood vessels, etc. from pulse wave information which is measured, and an operation program product for the processing apparatus.
2. Description of the Related Art
Conventionally, body weight, body fat, etc. are generally measured for health control purposes. Recently, the increasing health-consciousness of people causes a need to better understand the functional state of the circulatory system, especially the functional state of blood vessels and the blood flow, not just the blood pressure. In this respect, biological information processing apparatuses are known which are capable of measuring a photoelectric pulse wave by exposing a living body to red light and infrared light having different wavelengths and then measuring the light that has passed through (or reflected by) the living body owing to the fact, for example, that there is a difference in the respect of absorptive power between the hemoglobin and the oxygenated hemoglobin present in blood. Japanese Unexamined Patent Publication No. HEI5-200031 discloses the technology used in such biological information processing apparatus that calculates an estimated age of blood vessels by extracting, as characteristic points, a maximum value point and a minimum value point of an acceleration pulse wave which is obtained by taking the second derivative of a pulse wave.
However, the acceleration pulse wave has generally many noise components because it is obtained by taking the second derivative of the pulse wave. Also, the acceleration pulse wave is vulnerable to external disturbances because such point information as maximum value and minimum value is used as characteristic quantity as mentioned above. In other words, a slight variation occurring in the pulse wave (or acceleration pulse wave) causes a large error in the evaluation or deviated evaluation value which hinders the stable operation of the apparatus, and hinders the stable measurement and arithmetic processing. In order to avoid these problems, it is necessary to execute additional operations, for example, prolonged sampling, preprocessing such as filtering. Consequently, the conventional apparatuses unavoidably have the problems that the processing requires much longer time due to the complexity.